Thorough Analysis of mm-Wave Broadband Planar and Vertical Transitions for Loss Reduction of Interconnects in Multilayer PCBs

This paper presents a comprehensive investigation of mm-wave broadband planar and vertical transitions in multilayer printed circuit boards (PCBs) for high-density interconnects. The study focuses on microstrip to microstrip/stripline transitions across thin and thick substrates, addressing challenges related to chip/package attachment with small pitch sizes, the use of additional interfaces like interposers, as well as metallic losses and signal integrity. Planar transitions employ a tapered structure to connect microstrip to microstrip and stripline to stripline traces for the purpose of reducing metallic losses. Vertical transitions utilize vias to connect microstrip to stripline traces, with careful consideration of via diameter and anti-via diameter to maintain a $50 \Omega$ characteristic impedance. Through meticulous analysis, the proposed designs exhibit excellent performance up to 60GHz, achieving a return loss better than $10 \mathrm{~dB}$. These transitions offer efficient solutions for routing high-speed signals in multilayer, high-density interconnect PCBs, ensuring minimal losses and crosstalk at mm-wave frequencies.